The Back-side Surface Treatment ("BST") is a module that cleans the backside of a wafer just before a process on
the exposure system. To support immersion lithography, Tokyo Electron introduces a bevel cleaning function to
this module. This enables cleaning of both wafer backside and bevel section at the same time. We evaluate the new
BST module for wafer cleaning performance, wafer backside cleaning performance and wafer topside particle
control performance. The effectiveness of the BST module is tested in an actual production line. It is proved that the
introduction of the BST module reduces defocus and blocked images.
In the photolithography process, with the miniaturization of pattern size, depth of focus (D.O.F) is also becoming smaller
and smaller. This indicates that the control of particles on the wafer backside which has not been regarded as a problem
so far is becoming important.
Therefore, we considered that wafer backside is cleaned just before a wafer is transferred into the exposure equipment in
order to prevent the occurrence of a Focus error and reduce the contamination of the exposure chuck.
As a result, it was verified that the cleaning of wafer backside at the memory production line of the 70nm node can
reduce the contamination of the exposure chuck and can extend the period of maintenance for the exposure equipment.
Moreover, it was also verified that the cleaning of wafer backside can improve productivity.